RS-232 Tx / Rx monitoring LEDs?

Chuck Guzis cclist at
Sun Aug 23 10:56:52 CDT 2015

On 08/22/2015 11:55 PM, drlegendre . wrote:
> I've also seen C-R series voltage dropping circuits, here & there.
> Correct me if I'm wrong, but doesn't the series cap dissipate power
> just as it would, were it a series resistor? I mean, if the LED is
> passing 20mA, the cap is also doing 20mA - and at whatever the Vdrop
> is.
> Right? If not, why?

That's correct--but there's the matter of the voltage.  Eventually, 
you'll see that the brightness of the LEDs will drop fairly rapidly 
before the thing is useless.  A common dodge used by Chinese 
manufacturers.   Saves a few components, doesn't it.


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